A fixed displacement pump provides a theoretical fixed amount of oil per each revolution of the pump. Flow-rate is increased in proportion to the rotational speed of the pump. In practice, a limiting pump speed, or high speed fill limit (hereinafter HSFL), is reached when the pump chambers can no longer be completely filled with oil. Incompletely filled pump chambers introduce air into the oil giving rise to a two-phase mixture that potentially causes cavitation. The pump flow-rate levels off to become independent of further increases in the rotational speed of the pump; however, the cavitation phenomena can cause pressure instability that interferes with the transmission control valves and potentially gives rise to objectionable noise. In more severe forms, the collapse of the air bubbles at sonic velocities can cause physical damage to the pump itself.